1. Field of the Invention
The present invention relates to a mobile radio communication system and, more particularly, to a method of detecting the location of radio terminal equipment such as a portable telephone set.
2. Description of the Prior Art
Recently, small and light-weight portable telephone sets have been developed and widely used. Since such a portable apparatus is designed to be transported easily from one location to another, in some cases, it is very important to detect where it is located. Accordingly, there have been proposed a variety of ways to detect the location of a portable telephone set.
A conventional method is disclosed in Japanese Patent Unexamined Publication No. Hei 2-285730. The method is to specify the location of a portable telephone set depending on which one of receivers each having a certain location has received a predetermined radio wave from the portable telephone set.
Another conventional method is disclosed in Japanese Patent Unexamined Publication No. Hei 3-117225. In this method, a searcher having a directional antenna is used to receive a radio signal from a pocket bell while moving, the searcher specifies the location of the pocket bell.
However, in the first conventional method, location detection is made by the receiver that has received the radio wave from a portable telephone set, so a large number of receivers must be installed to increase the accuracy of detection. Therefore, this conventional method can be applied only to a limited area such as a room.
Also, in the second conventional method, since a pocket bell emitting a radio signal is searched for by means of the searcher having the directional antenna, the searcher must be moved while the direction of the directional antenna is being changed or, alternatively, a plurality of searchers are required. Therefore, this conventional method cannot be applied to a wide service area.
It is, accordingly, an object of the present invention to provide a method of detecting the location of a mobile terminal without reducing advantages of mobile communication services available in a wide area.
It is another object of the present invention to provide a method capable of specifying the location of a mobile terminal as well as tracing it.